Recorder for electrical quantities



NOV. 9, 1954 K 2,693,990

RECORDER FOR ELECTRICAL QUANTITIES Filed June 5, 1952 2 Sheets-Sheet l r I fig. 4a.

z 0' I INVENTOR fieorg'e fi'. fink ATTORNEY Nov. 9, 1954 G. A. FINK RECORDER FOR ELECTRICAL QUANTITIES 2 Sheets-Sheet 2 Filed June 3, 1952 INVENTOR ATTORNEY United States Patc'IItGfi ice Patented Nov. 9, 1954 The present invention relates to recorders for electrical quantities, such. as currents .and potentials-r Ohenobject. of this invention. is.:-to provideaa direct-1 writing recorder. capable of. accurately ,recording rapidly. varying values, in particular, to extend the .frequency responseof. the recorder. to higherfrequencies than=those obtainable with .known vmethods, -.while. retaining good response. to steady inputquantities.

Another object of this inventionais to provide-:means-v for suppressing hunting or overshooting thus giving,.-goodtransientresponse.

A further object of the .present invention is to-produce arecorder. which'may be easily given an arbitrary record-. ing. characteristic, orarbitrary relation between the elec-. tricahquantity tobe recordedand the recorded coordinate. or. position of the recording stylus.

Previously known direct writinggrecorders have gener.-. ally beeniof two types: (1) the direct-deflection type, using. .,a movingcoil, piezoelectric crystal, or -.magnetic drive for therecordihg stylus or=pen,and (2) the servo;- operated type in which. a primary moving element; such. as a galvanometer coil, .is-- held to *an essentially; zero defiectionby aifeedback system and .somenpart .of the fe'edhacksystem .-is provided :with means for-recording; and frequently alsois provided withmeans' for controlling; some quantity vor process.

Recorders ofathe first type have rather :limited sensitivity and speed, while the'piezoelectricvcrystal' type will not recordsteady values differentzfrom zero. Also; these recorders cannot-have their recording characteristics eas ily changed; The second 'type is moresensitive-:and. accurate, .butis much slower. My inventioncombines thetadvantages of .-both of these-..types,-.having the sen-.. sitivity andv accuracy of the servo-operatedtypeialong with. speed 7 at least type.

My invention uses anarnplifier and photoelectric actuatedby a .movingcoil-in a feedback loop to:controlthepositionof the-moving-; coilin. accordance with the:

electricaL-quantity beingarecorded. somewknown ree 7 in Reissue -.--Patent- .No."

corders; such :as that described 20,476, use" photoelectricafeedback devices; but they-tare: used for keeping thedeflection of the. :moving TCOflf-tO. an? essentially zero value, while myinvention keepsrzthe net.

input-voltage. to 'anamplifier essentially zero,. and makes the'deflection .of the coil essentially equalito some desired.

functionof the quantity to .be recorded;v

The presentinventionis similar to my copendingappli cation SerialNotSSAlO, filed November-5,- l948gin that theaposition-iof thernoving .coil of -.a.:recorder. is "con; trolledeby feedback; In .that invention the feedback ivolt= age isgenerated by strain-sensitive resistors mounted :on -':a' member "deform-:- able by movementof the coil." of-feedback used in the present invention *willzaccomplish the; :same. purpose, impose le'sst restraint on the moving coil,1-and allow of easy change of-recording characteristic.

Thefabove and other featuresaand objects of my invention twill be apparent from' the Fig; 2 shows a modification of the optical Isysternnof Fi'gg l 'to give nondinearresponse;

Fig'. -;3 shows amod-ific'ationof the apparatus shown in.

as high as .tha-tof the -.direct-deflectionabridge circuit. whose "arms are The photoelectric: method following description of 5 certain'ernbodirnents thereof;reference-being made to the Fig l, with two photocells.land-networks to allow-opera;

tion on either polarity of asig Fig; 4-shows azmodification' of the-optical system of Fig;-. 1, usingza mirroriin place of-arshutter to. vary the amount of'lig'ht reaching the phototube;'and

Fig. 4A is another View of theopti'cal system:of:Fig. ;4;

showing; how rotation' of :the-

mirror varies the. amount of light reaching thephotocell.

In .the form of my-inventionshownin Fig.4, a movingcoil '1 is supported; bygbea rings or suspensions 2,- ofnegligible'. restoringtorque, and its terminals are con-\ nectedwto thecoutput terminals to. the coil; andnrotatinggwith it; are twoarmsgone carrying a :stylus 54-and -the.other carrying ;a shutter or vane 5. The ..stylusi is adapted -to:record in ElllYg'kl'lOWIl manner, as for example on astrip of paper 6; as it passes over a-roll '7. The shutter is'arranged to intercept-light from a-lamp; 8-.-and condenser lens 9 projected-.:toward= a :diffusingwindow 10 tube 12. The anode in. a box 11 containing'gaaphoto-i lead 13.

and the cathode lead 114 tromthe'phototuhe are connected 'to a networkicontaine.

mg, in series; a battery 15 and two i resistors 16- and..-17.-'

The 'junctionsof the battery, and1resistor116 .is connected to one ofitheterminals to which .the input signal is applied:

This terminal maybe grounded, as shown. The :other signal input. a terminal -19"isone of the input terminals ofan 'ainplifier designed for differential input, ii. e. one1 which. is sensitiveto 1ts. input: terminals.-

a v difierencenof potential. between: The other input terminal: 20 0f the:

amplifiernis connectedito the junction of resistors .161 and 17 by means of: resistor 21,.and to-the junction'of'resistor' 17 andianode lead.13.by,-means of acapacitor 22;-

To understand'the operation of a recordingdevicecon-x structed =as-v described above, I consider first the zerocon dit1on-.-with-. no-signalwvoltageapplied to'terminals 18 and'vl9, anchwith:

the-.coil-and shutter in position -to'inter cept. allthelightprojected bylens 9 toward window'- 10:: There will; through resistors then-:be v no pho'totubecurrent 'flowingr 16 'and- 17, and novoltage droptin.-them;. The net. input tothe amplifier willhence also the output'will be zero;

then be: zero, and: so that no .:current'- and no torquewill be actingon 'it.'- Thewholesystern is then in a state of equi librium It a difference of and 19, terminal 18 potential is appliedto "terminals 18-. beingipositivewith respect to '19,

the .net. input totheiamplifier willvno longer be Zero. and:

an-"outpub current the-.rnoving coil.

netic field in which the coil torquethat will-rotate the co and shutter;

will flow from the amplifier through This current will react with the -mag= is mounted 'toi produce 1 a 11 with i :its attached stylus Motion of shuttersS will uncover window" lit, allowing light to-. strike the window and illuminate the cathode ofirthe phototubes A photocurrent approx? mately-proportionalto the: area 'of window l0iwhich' has .beennuncoveredwill then :flow'through resistors-:16:-

midi-17,- producingga :voltage dropginnthem proportional to-.the photocurrent, and hencezproportional to .the1rota-' tion .o'f-fthe Ishutte'r,

stylus;- The voltage idrop:

in resistor l6- will be of -the-proper'polarity to oppose a.

negative t input signal ference at. the amplifier input assumed, thepotential dit"-' will bef decreased. o This" action will:continue until the-yoltageidrop'in resistor 16 1S equalnin. magnitudetoithe --applied signal, when. the' system willnagainsbe in-equilibrium. if the :coil 1 is not rotating- If 'the coil is rotating in photocurrent, the :..voltage direction to increasewthe- :drops in resistors 16 and'17 will be-inc-reasing;andflthe :ditferentiatirigi circuit composed-of resistor ZI-and capacitor-.22.:will apply-to the amplifiernnput terminallq'la voltage approximatelypro portional to .tneurate resistor 17, in addition ofchange-of the voltage rlropl'in to the voltage drop in resistor 16.

This added-ivoltagewill unbalancethe amplifier input and-cause current to-tlowfrom the amplifier output through, coil l. in 'the'direction' to oppose the coil motion.

Thus, a damping effect isobtained whosexrnagnitude can lac-adjusted by varying the --rati l6,- andnthe.tiniezconstantthewdifferentiating .cir-

cuit 21, 22 maybe-adjusted to istics .of coilal andzarnplifier 3 00:? resistor 17 totresisto'r' fit the dynamic character-' in order. to produce-opti mum damping. With optimum damping the recorder will attain equilibrium after a change of input voltage as rapidly as possible without overshooting.

For each value of input voltage within the range of the recorder there will be a position of the coil, stylus, and shutter system at which the voltage drop in resistor 16, due to photocurrent through it, will balance the 1nput and produce equilibrium. With the optical system shown in Fig. 1, the motion of the stylus will be linearly proportional to the input voltage.

To obtain non-linear response, the modification shown in Fig. 2 may be used. The shape of the window 10' is changed so that its width in a direction measured radially outward from the axis of the coil is no longer constant. The area of window 10 uncovered at a given position of the shutter, coil, and stylus, is made proportional to the value of input voltage required at that position for the recorder to follow a specified characteristic.

In order to be able to record signals of both polarities, the optical system and coupling network may be modified as shown in Fig. 3. The lamp 8, lens 9 and shutter are arranged as in Fig. 1, but two phototubes 12a, 12b are provided in a box 11a with two windows a and 10b, and the coupling network is duplicated. The phototube cathodes are connected by conductor 14 to the negative terminal of a common battery 15, and the anodes are connected through equal networks 16a, 17a, 21a, 22a and 16b, 17b, 21b and 22b, similar to the single network in Fig. 1, to the positive terminal of battery 15.

The zero position of shutter 5 is now such that equal areas of the windows 10a and 10b are uncovered. In this position, assuming phototubes 12a, 12b have equal sensitivities, the photocurrents will be equal, and the voltage drops in resistors 16a and 17a will be equal, respectively, to the voltage drops in resistors 16b and 17b. The polarities are seen to be such that the potential difference between terminals 18 and is zero, so that the system will be in equilibrium with zero input.

When the shutter 5 moves in one direction from its zero position, it uncovers more of one window, and less of the other, increasing the photocurrent from one phototube, and decreasing that from the other. The voltage drops in resistors 16a and 17a will no longer equal that in resistors 16b and 17b, so that the potential ditference between terminals 18 and 20 is no longer zero. The system will be in equilibrium now if the input voltage is equal to the potential difference between 18 and 20 and has a polarity such that the net input to amplifier 3 is zero. If the signal polarity is reversed, there will be another equilibrium position with shutter 5 on the opposite side of its Zero position. The coil motion will be damped as equilibrium is aproached just as in the arrangement shown in Fig. 1, since similar coupling networks are used.

A further modification is shownin Figs. 4 and 4a, in which a mirror 23 fastened to the coil 1 takes the place of the shutter in the arrangement of Figs. 1, 2 and 3. Lamp 8 and lens 9 project a beam of light toward the mirror 23 from which the beam is reflected toward a box 11 containing a difi'using window and phototube as shown in Fig. 1. Fig. 4a is another view of part of the optical system of Fig. 4, looking parallel to the axis of the coil, which shows how the rotation of the mirror changes the amount of light falling on the window 10, and thus varies the photocurrent from phototube 12. The circuit connected to the output of the phototube assembly 11 may be the same as in Fig. l or 3. The operation is similar to that of the arrangement shown in the preceding figures, and it will be apparentdthat a modification corresponding to Fig. 2 may be ma e.

While the invention has been described with reference to certain specific embodiments, it is to be understood that the same have been given merely by way of illustration, and not as a limitation upon the scope of the invention as defined in the appended claims.

I claim:

1. A recorder comprising an amplifier having a pair of input terminals, means for impressing an input signal on said amplifier, electromechanical transducing means connected to the output of said amplifier, recording means actuated by said transducing means, photoelectric means, optical means connected to said transducing means for illuminating said photoelectric means said transducing means controlling said optical means to produce and maintain for the duration of an input signal an amount of illumination corresponding to the amplitude of the input signal, an output circuit means connected to said photoelectric means for impressing between said amplifier input terminals the output voltage of the photoelectric means in series with the input signal but with a polarity opposite to the polarity of the input s1gna 2. A recorder according to claim 1, wherein the transducing means includes a galvanometer coil and means for supporting said coil for rotary movement with negligible restoring force.

3. A recorder according to claim 1, wherein the optical means includes a light, a shutter interposed between said light and said photoelectric means, said shutter being attached to said transducing means for movement therewith to vary the amount of light on the photoelectric means in accordance with the position of said transducing means.

4. A recorder according to claim 1, wherein the optical means includes a light and a mirror mounted on said transducing means for reflecting light onto said photoelectric means.

5. A recorder comprising an amplifier having a pair of input terminals, means for impressing an input signal on said amplifier, electromechanical transducing means connected to the output of said amplifier, recording means actuated by said transducing means, photoelectric means, optical means connected to said transducing means for illuminating said photoelectric means in accordance with the position of said transducing means, an output circuit connected to said photoelectric means, said output circuit including means for impressing between said amplifier input terminals a voltage in series with the input signal but having a polarity opposite to the polarity of the input signal, and means for supporting said transducing means with a negligible restoring force, whereby said voltage has a magnitude substantially equal to the magnitude of the input signal at the rest position of said transducing means.

6. In an electrical recording device, the combination of: two signal input terminals, an electrical amplifier sensitive to difierences of potential between its two input terminals, with the first of said amplifier input terminals connected to the first of said recorder input terminals, electromechanical transducing means connected to the output of said amplifier, recording means actuated by said transducing means, a light source, photoelectric means, optical means actuated by said transducing means for varying the amount of light transmitted from said light source to said photoelectric means in accordance with the position of said transducing means, a source of electric current, a first resistor and a second resistor connected in series with said source and said photoelectric means, with the second of said recorder input terminals connected to the junction of said source and said first resistor, a third resistor connected from the junction of said first resistor and said second resistor to the second of said amplifier input terminals, and a capacitor connected from the second of said amplifier input terminals to the junction of said second resistor and said photoelectric means.

7. In an electrical recording device, the combination of: two signal input terminals, an electrical amplifier sensitive to differences of potential between its two input terminals, with the first of said amplifier input terminals connected to the first of said recorder input terminals, electromechanical transducing means connected to the output of said amplifier, recording means actuated by said transducing means, a light source, a first photoelectric device and a second photoelectric device each having at least two electrodes, optical means for varying the amount of light striking said two photoelectric devices difierentially in accordance with the position of said transducing means, a source of electric current having one terminal connected to like ones of said electrodes, a first resistor and a second resistor connected in series with said current source and said first photoelectric device, a third resistor and a fourth resistor connected in series with said current source and said second photoelectric device, a fifth resistor connected from said second recorder input terminal to the junction of said first resistor and said second resistor, a first capacitor connected from said second recorder input terminal to the other electrode of said first photoelectric device, a sixth resistor connected from said second amplifier input terminal to the junction of said third resistor and said fourth resistor, a second capacitor connected from said second amplifier input terminal to the other electrode of said second photoelectric device.

8. A recorder according to claim 7, wherein the transducing means includes a galvanometer coil and means for supporting said coil for rotary movement with negligible restoring force.

9. A recorder according to claim 7, wherein the optical means includes a light, a shutter interposed between said light and said photoelectric means, said shutter being attached to said transducing means for movement therewith to vary the amount of light on the photoelectric means in accordance with the position of said transducing means.

10. A recorder according to claim 7, wherein the optical means includes a light and a mirror mounted on said transducing means for reflecting light onto said photoelectric means.

11. A system comprising an amplifier having a pair of input terminals, means for impressing an input signal on said amplifier, electromechanical transducing means connected to the output of said amplifier, photoelectric means, optical means connected to said transducing means for illuminating said photoelectric means in accordance with the position of said transducing means, an output circuit means connected to said photoelectric means for impressing the output voltage of the photoelectric means between said amplifier input terminals to provide a voltage in series with the input signal but having a polarity opposite to the polarity of the input signal.

12. A system comprising an amplifier having a pair of input terminals, means for impressing an input signal on said amplifier, electromechanical transducing means connected to the output of said amplifier, photoelectric means, optical means connected to said transducing means for illuminating said photoelectric means in accordance with the position of said transducing means, an output circuit connected to said photoelectric means, said output circuit including means for impressing between said amplifier input terminals a voltage in series with the input signal but having a polarity opposite to the polarity of the input signal, and means for supporting said transducing means with a negligible restoring force, whereby said voltage has a magnitude substantially equal to the magnitude of the input signal at the rest position of said transducing means.

13. In an electrical system the combination of two signal input terminals, an electrical amplifier sensitive to diiferences of potential between its two input terminals, with the first of said amplifier input terminals connected to the first of said signal input terminals, electromechanical transducing means connected to the output of said amplifier, a light source, photoelectric means, optical means actuated by said transducing means for varying the amount of light transmitted from said light source to said photoelectric means in accordance with the position of said transducing means, a source of electric current, a first resistor and a second resistor connected in series with said source and said photoelectric means, with the second of said signal input terminals connected to the junction of said source and said first resistor, a third resistor connected from the junction of said first resistor and said second resistor to the second of said amplifier input terminals, and a capacitor connected from the second of said amplifier input terminals to the junction of said second resistor and said photoelectric means.

14. In an electrical system, the combination of: two signal input terminals, an electrical amplifier sensitive to differences of potential between its two input terminals, with the first of said amplifier input terminals connected to the first of said signal input terminals, electromechanical transducing means connected to the output of said amplifier, a light source, a first photoelectric device and a second photoelectric device each having at least two electrodes, optical means for varying the amount of light striking said two photoelectric devices differentially in accordance with the position of said transducing means, a source of electric current having one terminal connected to like ones of said electrodes, a first resistor and a second resistor connected in series with said current source and said first photoelectric device, a third resistor and a fourth resistor connected in series with said current source and said second photoelectric device, a fifth resistor connected from said second signal input terminal to the junction of said first resistor and said second resistor, a first capacitor connected from said second signal input terminal to the other electrode of said first photoelectric device, a sixth resistor connected from said second amplifier input terminal to the junction of said third resistor and said fourth resistor, a second capacitor connected from said second amplifier input terminal to the other electrode of said second photoelectric device.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,822,075 Aronoif Sept. 8, 1931 2,077,451 Wilson et a1. Apr. 20, 1937 2,113,436 Williams, Jr. Apr. 5, 1938 2,243,456 Dulter May 27, 1941 2,367,614 Rich Jan. 16, 1945 2,507,301 Fulbright May 9, 1950 2,547,662 Rich et al. Apr. 3, 1951 

